The present invention relates to a control device for a vehicle equipped with an engine, a motor and a generator.
In recent years, the use of hybrid vehicles equipped with an engine a motor and a generator is becoming more common due to demand for low pollution, longer travel range and an infrastructure for energy supply. The parallel hybrid vehicle (referred to hereafter as PHEV) which is already in practical use mainly runs on the engine, and increases fuel cost-performance by assisting the driving force by the motor using the power recovered during deceleration, etc.
On the other hand, there is also a series hybrid vehicle (referred to hereafter as SHEV) which aims at much higher efficiency. In an SHEV, the vehicle is driven only by the motor and the engine is used only for driving a generator. The SHEV as conventionally proposed makes the enhancement of efficiency its primary goal, so the engine is operated under certain fixed conditions for which fuel-cost performance is optimized.
However, in such a SHEV, as it is necessary to vary the running state of a vehicle without changing the driving state of the engine, a battery of sufficient capacity is needed, and an increase of weight and cost cannot be avoided.
The Inventors therefore proposed a hybrid vehicle having the same mechanical structure as a SHEV, i.e., an engine, a motor and a generator, wherein the power consumed by the motor for vehicle running is computed at every instant, and the engine and generator are controlled to generate sufficient power for this. If the power consumed by the motor and the power generated by the generator are in agreement, only a minimum capacity is required, the battery which is a factor leading to increased weight and cost can be made compact, and costs can be suppressed.
However, as the power consumed by the motor and the power generated by the generator are no longer in agreement when the running state of the vehicle changes suddenly, such as when the driver depresses the accelerator pedal abruptly, for example, a battery which has a capacity which can compensate for the excess or deficiency must be provided.
Such an excess or deficiency arises when the running state changes suddenly, because, even if a command is given simultaneously to the generator and engine that the power generation amount should be adjusted, the response of the engine is very slow compared with the response of the generator. For example, even if a command is given to increase the rotation speed of the engine and generator to increase the power generation amount corresponding to the increase of drive torque, as the engine response is slow, the generator whose rotation speed is controlled generates a drive torque using the battery power and the rotation speed increases before the rotation speed increases due to increase of engine torque. As a result, the power generation amount of the generator temporarily decreases although it is necessary to increase the power generation amount, and the generator also consumes an excessive amount of power, so the difference between the power generation amount and the power consumption increases.
If filtering is performed on the command value to the generator to delay the apparent response of the generator, as disclosed in JP-A-H11-122710 published in 1999 by the Japanese Patent Office, power consumption by the generator can be suppressed. However, although the response of the generator is delayed by the filter, the driving power output of the motor increases immediately, so the discrepancy between the generated power and the power consumption is not eliminated.
Is therefore an object of this invention to make the power consumed by the motor coincide with the power generated by the generator even if the running state of the vehicle changes suddenly, and to further reduce the required battery capacity.
In order to achieve above object, this invention provides a control device for a vehicle, the vehicle comprising an engine, a generator connected to the engine, and a motor driven by the power generated by the generator, connected to a drive shaft of the vehicle, and the control device comprising a sensor which detects a vehicle speed, a sensor which detects an accelerator depression amount, and a microprocessor. The microprocessor is programmed to compute either of a target driving force and target output torque of the motor based on the vehicle speed and accelerator depression amount, compute a delayed target output torque of the motor by performing a delay processing on either of the target driving force and target output torque, and control the torque of the motor based on the delayed target output torque.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.